1. Field of the Invention
The disclosed mechanism relates in general to a waveguide configuration, and more particularly, to a waveguide configuration which is particularly well suited for the suppression of SBS due to an interaction of acoustic waves with optical signals.
2. Technical Background
The use of waveguides in various industries such as telecommunications and lasers, among others, has been steadily increasing. While the ability to send optical signals through waveguides is well known in the art, certain deleterious phenomena have been observed. In particular, one generally undesirable effect that has been observed is the Stimulated Brillouin Scattering (SBS) effect. SBS is one of the major limiting factors on the amount of power that can be transmitted via an optical fiber.
SBS is an interaction of optical energy with acoustic energy. Optical energy guided into optical waveguides, e.g., the core of an optical fiber, produces acoustic energy. As is known in the art, once a certain amount of optical power is directed into a waveguide from another optical source or generated in the waveguide, the effect of SBS causes optical energy to backscatter into the source. This phenomenon has become relevant in the optical fiber industry, due to the increasing intensity required in optical fiber cores and the relatively long interaction lengths.
Some attempts to suppress the SBS effect relied on waveguides with particular constructions. While some of the solutions have suppressed the SBS effect to some extent, many of these waveguides have constructions which are difficult to manufacture on a large scale, or which are economically not feasible.
U.S. Pat. No. 6,856,740 and U.S. Pat. No. 6,687,440 disclose the use of acoustic field antiguiding to reduce SBS. This is achieved by an optical fiber core that is doped such that the longitudinal acoustic velocity of the fiber core is higher than that of the cladding. However, our analysis showed that this technique will have limited utility because in certain circumstances the acoustic wave in a typical acoustically antiguiding fiber can be guided in the core.
U.S. Pat. No. 7,130,514 discloses a fiber configuration with mode field diameter greater than 12 micrometers and delta % difference between the peak core delta and the cladding of less than 0.3%. The acoustic profile having at least two adjacent regions with acoustic field velocities differing by at least 0.2%. According to its written description, this invention deals with acoustic cladding modes that are prevalent in the absence of core modes. The acoustic cladding modes couple into the core, creating SBS and establishing the SBS threshold.